1. Field of the Invention
This invention relates to a microwave antenna element, and in particular, although not exclusively, to an antenna element for use in cavity-backed dual-slot antennas for circular polarisation.
2. Description of Related Art
Conventionally, when it is required to produce circular polarisation from such antennas, either a pair of orthogonal probes is used in conjunction with each pair of slots, or a single probe is used to feed a form of resonant patch in the centre of the cavity. Two such antennas using orthogonal probes are described in U.S. Pat. Nos. 4,626,865 and 4,486,758. However, these types of arrangements are limited in their use because they inherently operate over a narrow axial-ratio bandwidth, typically 1%.